P2P networks are widely used for the distribution of digital content over the public internet. Contemporary P2P networks are generally unregulated. Unregulated P2P networks such as BitTorrent and eDonkey operate as decentralised overlay networks running over TCP/IP protocol. In such networks there is no definitive central server.
Discovery of remote peers is performed using such overlay networks. Decentralised P2P networks normally use distributed hash tables (DHTs) to implement the mechanism to discover which peers hold a particular file. One difficulty with this approach is that using DHTs it is only possible to perform exact-match searches rather than keyword searches however, while keyword search functionality is not supported directly by DHTs, it can generally be layered over them. BitTorrent uses trackers to facilitate the discovery of peers—a BitTorrent tracker is server software which assists in the communication between peers using the BitTorrent protocol.
Unregulated P2P networks for sharing digital content have been popular with users, but very unpopular with content providers. Without a central server acting as an authority, unregulated networks are unable to perform a number of functions that a content provider would desire. For example, there is no control over authenticity of content downloaded, or who downloads from whom, no way to make newly available peers immediately available to existing peers and no way to provide effective balancing of peer-to-peer network traffic load
Some of the concerns of content providers can be met by regulating the P2P network, and this can allow for payments to be made to content providers. A regulated peer-to-peer network, such as Napster, involves a central authority to verify that a purchase has been made. A user obtaining content through the network participates in it as a downloading peer. If a downloading peer requests a file that the associated user has found (this may have been indexed in a central index associated with the central authority, or through DHTs), it must then make a payment to the central authority. If the payment is successful, the central authority, when queried by an uploader, can confirm that a downloading peer is authorised to download a particular file. The central authority will provide a list of Internet Protocol (IP) addresses of various uploading peers which currently are online and which store the file, and who will upload that file to the downloading peer. The downloading peer subsequently contacts the uploading peers and requests the file. The uploading peers check with the central authority to verify that payment has been made, then the downloading peer downloads part of, or the entire file from each uploading peer.
One problem associated with such regulated P2P networks is that they are unattractive to users. Users will not subscribe to such regulated networks, in which content is purchased, because such content is widely available without charge on unregulated networks.
One proposed solution to this problem is to provide an incentive for users to join a regulated network in which legal file sharing can be enforced. This is achieved by rewarding those who participate in file sharing. One such arrangement is shown in EP 1348151 A2, in which a payment is made to a central authority for downloading a file, but in which a payment is also made to an uploading peer for uploading the file for download by the downloading peer.
The availability of a reward structure of this kind provides a disincentive for an uploading peer to make their library of content available over an unregulated P2P network, as it will not be rewarded for providing its legitimately owned content over such a network.
However, there are many technical hindrances to implementation of P2P networks, especially those which are regulated and set up to reward user participation.
For example, in a regulated P2P network, users need to pay for the content that is downloaded. Therefore there are significant security and accountancy considerations related to authenticating the purchase of content.
Furthermore, it is necessary to be able to efficiently propagate content from peer to peer on the network for the purposes of making that content widely available in a short amount of time. This is particularly challenging in view of the constraints of a peer-to-peer network that is regulated. Building in functionality associated with regulation tends to work against maximising content propagation.
A system is required that is capable of alleviating the above-mentioned problems.